Enigma and Seer are really good for sure, but a bit unreliable, both because of the difficult positioning of their ulties. Maybe you can say the same for SK.

Easiest, most powerful and most reliable teamfight heroes/initiators are probably ES and Tide. Perhaps Rooftrellen, but aside from his ulti, he doesn't really add anything to the teamfight, while ES has another 2 stuns and Tide has minus armor, minus damage, and can also deal damage himself.